Measurements of the static pressure around in actual residence

Abstract

Dutch standard 1078 gives directions for correctly locating the outlets from chimneys. These directions are based on pressure-difference measurements taken around model houses in a wind tunnel some ten years ago. These pressure differences were measured in a vertically standing pipe without a cowl, thus the pressure difference was not equal to the static pressure. This was the result of an addition hereto through a suction or stagnation condition prevailing at the top of the pipe. The transition from a stagnation to a suction condition occurs within some tens of degrees of the angle of incidence. Due to this degree of sensitivity, these results cannot be used for chimneys with cowls. As an illustration of the difficulties encountered, a case is presented in which the residence is provided with a chimney for a fireplace located in accordance with the criteria laid down in the NEN standard herefor. The problem to which all the houses were subjected was the downdraught in the chimney whenever the wind blew towards the chimney side of the houses. Thus house buyers demanded a solution to this problem from the builders. In persuance of this requirement, TNO was commissioned to find the correct solution to the problem and in consequence a model was tested in a wind tunnel to evaluate the proposed solution to the problem. Pressure differences were measured in a vertically standing pipe and with a specially developed probe. The wind-tunnel test confirmed the idea that in order to correctly evaluate the proper place for the chimney outlet, one requires to know the prevailing static pressure and the local wind velocity to calculate the suction effect at the cowl's mouth. The air-flow directions turned out to be unimportant since the permitted types of cowl provide an almost constant suction, independent of the local wind direction.